The present invention relates to a new and improved method for the determination of the length of endless filamentary materials, herein referred to broadly as yarn, which is wound upon a cross-wound package at a winding apparatus or winder containing a friction drive and a grooved drum.
There are already known to the art, for instance, different methods and apparatuses for the continuous measurement of the length of a yarn during the winding thereof onto a rotating core or bobbin. Generally, there are usually formed so-called cross-wound packages, wherein the infed yarn is moved back-and-forth in axial direction of the cross-wound package by means of a yarn or thread guide or a grooved drum. With most of the modern winding machines the cross-wound package is driven by the grooved drum due to frictional contact. Significant in this regard are Swiss Patent No. 568,233 and German Patent No. 2,351,463. The length measurement is predicated upon the continuously measured number of revolutions and the diameter or circumference, as the case may be, of the grooved drum. Further techniques for measuring the length of a travelling endless yarn have been disclosed in British Patent No. 1,480,398.
At the conventional high rotational speeds of the driving grooved drum there is unavoidable an appreciable slip, in other words the trailing of the cross-wound package in relation to the grooved drum. As measurements of the assignee of this application have demonstrated, this slip is not constant during the winding operation. Therefore, it is not possible to obtain an exact correction factor for the entire winding operation by simply carrying out an initial test run as contemplated by German Patent No. 2,216,960, during which time there is measured the yarn length which has been wound-up during one revolution of the grooved drum. Also, heretofore there has not been given any definition of the slip and also there has not been devised any method for the continuous measurement thereof during the winding operation, and probably its significance in this regard has also not been fully appreciated.
In U.S. Pat. No. 4,024,645 there is disclosed a method for continuously determining the length of a wound package at a winding machine having a positively separated drive of the cross-wound package and a thread guide which causes a changing movement of the wound-up yarn. For this purpose there are continuously measured and evaluated the number of revolutions of the cross-wound package and its diameter or circumference. Since with the described winding machine there is not present any slip between the cross-wound package and the thread guide it is also unnecessary to undertake any slip correction at the length measurement.
It might be conceivable to employ the method known from the aforementioned U.S. Pat. No. 4,024,645 also at a winding machine having a friction drive of the cross-wound package by means of the grooved drum, in order to eliminate the effect of slip upon the length measurement. While this would result in an increased accuracy, nonetheless the full effect of the slip would not be taken into account. This will be considered in greater detail hereinafter in conjunctibn with the description of the exemplary embodiments.